How to add sortable functionallity to the DataTable...

[Aimee Bailey]

In work today I was asked weather it was possible to sort a DataTable via column index, so while looking through the DataTable method list, I was surprised to find nothing but the simple DataTable.Select method.

Luckily in .Net we can inherit classes, so it is not hard to implement a custom sort feature. here is how I did this:

Public Class SortableDataTable
       Inherits DataTable
 
    Public Sub Sort(ByVal columnIndex As Integer, _
                    ByVal direction As dDir)
        Dim result As New List(Of DataRow)
        Select Case direction
            Case dDir.Ascending
                Dim v = From r In Me.Rows _
                        Order By r(columnIndex) _
                        Ascending
                For Each row In v
                    Dim nr As DataRow = Me.NewRow
                    nr.ItemArray = row.ItemArray.Clone
                    result.Add(nr)
                Next
            Case dDir.Descending
                Dim v = From r In Me.Rows _
                        Order By r(columnIndex) _
                        Descending
                For Each row In v
                    Dim nr As DataRow = Me.NewRow
                    nr.ItemArray = row.ItemArray.Clone
                    result.Add(nr)
                Next
        End Select
        Me.Rows.Clear()
        For Each row In result
            Me.Rows.Add(row)
        Next
    End Sub
 
    Public Sub New(ByVal source As DataTable)
        If Me.Columns.Count <> source.Columns.Count Then
            For Each c As DataColumn In source.Columns
                Me.Columns.Add(c.Caption)
            Next
        End If
        For Each r As DataRow In source.Rows
            Dim nr As DataRow = Me.NewRow()
            nr.ItemArray = r.ItemArray.Clone
            Me.Rows.Add(nr)
        Next
    End Sub
 
End Class
 
Public Enum dDir
    Ascending = 0
    Descending = 1
End Enum
 

Adding this class to a project allows me to create a SortableDataTable, plus if I wish to apply this functionality to a table that already exists, I simply use the "New" constructor and pass in the table I want to sort like so...

Public Sub Button1_Click(sender as object, e as EventArgs)
    Dim newTable As New SortableDataTable(oldTable)
    newTable.Sort(0, dDir.Ascending);
End Sub
 

Unfortunately this way of going about things means you cannot cast a DataTable to an OrderedDataTable, however the reverse is possible. This means that if you wish to display your sorted data on a DataGridView for example, the DataSource property will also accept this type of class.

On a last note, I must admit there are probably easier ways to get this type of sorting implemented, however having an inherited class like this opens the possibility of advanced sorting.

Thanks for reading, and I hope it helps someone like it helped my colleague :)